This insert is made in our softest Red 65A durometer material, specifically for Diesel models, helping to limit NVH transmission. Designed to fill the voiding in the OE rubber mount, it smooths out gear changes and throttle application by stiffening and supporting the often perished rubber, a common failure on tuned vehicles. This supports a more precise and settled transmission response during acceleration and deceleration. This new part combines perfectly with our other Upper Gearbox Mounts and Lower Gearbox Mounts for greater engine stability. A small increase in NVH, usually at idle, should be expected when stiffening the connecting mount between the engine/transmission and chassis. The harder the material used, the greater the NVH transmitted.